Animal immune response may be closely tied to temperature

When a newborn pig is cold, it usually shivers. When that same cold piglet gets sick, it stops shivering.

Why is that?

According to Dr. Jeff Carroll, research leader for the USDA-ARS Livestock Issues Research Unit, temperature fluctuations and immune response work together to cause complex physiological reactions in livestock. In the case of the sick piglet, shivering stops because the piglet has to put all its energy toward fighting off the infection.

Piglets keep warm thanks to heat lamps. While this set-up can keep piglets healthy, Carroll explained that it is also important not to overheat the sow.

In a study of neonatal piglets kept at a chilly 18 degrees Celsius and a neutral 34 degrees Celsius, piglets showed a significant drop in ability to fight off disease when housed at the lower temperature. Immune response was measured by taking blood samples and recording rectal temperatures over three hours, and the pigs were given injections of Lipopolysaccharides as an immune “challenge”

“The pigs that were maintained in the warm environment exhibited no visual signs of illness.” Carroll said. But the cold pigs “redirected any nutrients they had toward survival.”

For example, when a sow gives birth, there is a risk that a piglet will get in the way and
the sow will accidentally crush it. This problem regularly leads to piglet mortality and economic losses for pig producers. While scientists already know that piglets often get too close to their mothers in an effort to keep warm, Carroll added that these cold piglets may also be showing signs of illness. He said producers need to keep piglets warm by providing heat lamps and heating pads at a safe distance from the sow.

Carroll also explained how understanding immune responses to temperature can help animal scientists get more accurate data. In addition to measuring rectal temperature, Carroll’s team also measured levels of cortisol, a stress hormone, in the piglets’ blood. They found that cortisol levels increased for the infected piglets in both the cold group and the neutral temperature group. The researchers also found that the cold, infected pigs had a significant decrease in body weight compared to the neutral temperature pigs.

These results are important for scientists to consider when conducting studies on livestock health. Carroll said that even when researchers are not studying the effects of temperature, they need to consider how temperature may skew their results. He said that temperature changes in nearly identical studies could lead to conflicting data.